Not Applicable.
1. Field of the Invention
The present invention relates to a system for determining the drilled distance between the surface and a point in a well bore. More particularly, the present invention relates to a system using a processor that calculates true measured depth based on data received from surface sensors, downhole sensors, and in another aspect, the present invention relates to a method for using a tubular umbilical to determine the drilled distance between the surface and a point in a well bore. More particularly, the present invention provides a method for correcting a surface-measured length of a tubular umbilical to determine the sub-surface length of the tubular umbilical by using an environmental profile to calculate length corrections. Still more particularly, the present invention relates to methods using temperature differentials, pressure differentials and axial loadings to correct a surface-measured length of a composite coiled tubing umbilical to determine the corresponding sub-surface length of the umbilical.
2. Background of the Invention
Successful hydrocarbon recovery operations are often founded on the ability to accurately log the trajectory of a drilled well bore extending hundreds or even thousands of feet below the surface of the earth. Accurate depth measurements can play an important, if not pivotal, role in such hydrocarbon recovery operations. Referring now to FIG. 1, xe2x80x9cmeasured depthxe2x80x9d (MD) is defined as a drilled distance between a surface point Po and consecutive points P1, P2 . . . Pn. In contrast, true vertical depth (TVD) is the distance between a point P and the surface point PO as measured on a vertical plane. Both MD and TVD are important for proper log data correlation. Because MD provides a basis for reference points along a drilled well bore, formation properties are often linked to accurate MD logs. With measurement-while-drilling (MWD) instrumentation, formation data such as gamma emissions and resistivity may be surveyed while a well bore is drilled. By logging the MD in conjunction with MWD surveys, formation data can be given a physical location with respect to the well bore trajectory. Once a well bore has been completed, a log for the well bore would show the formation properties at each MD. Such formation data can be used to determine which layers of formation are likely to hold hydrocarbon deposits. For example, it may be that the well log indicates that a gas layer exists at point Pixe2x88x921, an oil layer exists at point Pi (a xe2x80x9cpay zonexe2x80x9d), and a water layer exists at point Pi+1. Because oil is far more profitable to recover than gas, well owners often wish to drain the oil layer without disturbing the gas deposits above the oil. This is even more the case with water layers because recovery of water is rarely, if ever, profitable. Moreover, it is usually very undesirable to inadvertently drain a gas or water layer because these fluids tend to flood a well to such a degree that a well remains nonfunctional until all the water or gas has been evacuated from the well. Further compounding the inherent difficulties in this situation is that, in many instances, a pay zone may be less than fifty feet in a well bore that may be thousands of feet in length. Therefore, it is important that well owners obtain well logs having accurate measured depths for subterranean formations in order to drain a pay zone without disturbing adjacent layers.
Further, regulatory authorities often require that owners of wells keep detailed formation survey information. Inaccurate data could lead to unintended violations of regulatory rules and subject the well owner to fines or other penalties. Therefore, accurate MD logs provide the well owner with the information needed to comply with the rules governing drilling activities.
Obtaining accurate MD logs is usually a fairly straightforward process for wells using drill string made up of conventional steel pipe or steel coiled tubing. For conventional steel pipe, the individual joints making up the pipe string are of a known length. Thus, an operator needs only keep count of the number of joints making up the pipe string. For example, referring to FIG. 1, if one hundred joints, each thirty feet in length, span between point Po and point Pi, then the MD at point Pi is 3000 feet. Similarly, when steel coiled tubing 20 is used, the length of steel coiled tubing 20 payed out from a reel 22 on the surface represents the MD. Often, the length of steel coiled tubing is measured as a function of the number of revolutions made by a friction wheel (not shown); coiled tubing length may be also measured by other commercially available line payout devices. For example, referring to FIG. 1, a dial (not shown) on reel 22 may indicate that 3000 feet of steel coiled tubing 20 was payed out between points Po and Pi. Thus, the dial indicates a MD of 3000 feet at point Pi. In either of the above instances, as long as the surface measurements are taken properly, the MD should also be accurate. It should be understood that the examples discussed are merely illustrative and to not represent expected depth values or measurement accuracy.
While these prior art MD survey techniques may be reliable for tubing formed of metals such as steel, however, such techniques do not give accurate logs for tubulars made of materials such as composites. Composite materials for coiled tubing are discussed in pending application Ser. No. 09/081,961, filed May 20, 1998 and entitled xe2x80x9cWell System,xe2x80x9d which is hereby incorporated by reference. Tubulars made of non-metals, such as composites, are susceptible to significant length changes due to factors such as temperature, pressure and axial loadings. Unfortunately, elevated temperatures, high operating pressures and complex compression and tension loadings are almost always present in a well bore environment. Thus, a length of composite coiled tubing on the surface may expand or contract as it enters a well bore. For example, a surface-measured length at reel 22 may indicate that 3000 feet of composite coiled tubing was payed out at point Pi. However, the composite coiled tubing umbilical may have expanded to 3050 feet due to well bore conditions. Accordingly, the actual drilled depth at point Pi would be 3050 feet, not 3000 feet. An uncorrected MD log can present serious problems in later operations when equipment such as perforation charges are tripped downhole to initiate the drainage of a pay zone at Pi. Since this equipment is run in on a wireline or other device that is not subject to the same type or degree of expansion, the charge would be set at 3000 feet instead of 3050 feet, and possibly within the gas layer at Pixe2x88x921. Indeed, even during successive composite coiled tubing trips for the same operation, downhole conditions can vary to a point where it may be difficult to correlate logs of these successive trips. Despite the critical need for accurate MD logs, the prior art does not disclose systems or methods that correct surface measurements of tubulars made of materials that deform when exposed to environmental factors.
The present invention features a system and method for determining a sub-surface length of tubulars made of materials that deform when exposed to environmental factors. The sub-surface length of the tubing generally represents the measured depth. For a well having a composite coiled tubing umbilical extending from the surface to a bottom hole assembly in a well bore, an embodiment of a preferred system includes a surface processor, surface sensors, downhole sensors and a telemetry system. The surface processor includes software that determines an environ-mental profile for the tubing using the environmental data retrieved by the downhole and surface sensors. By applying the environmental profile to the surface-measured length of the tubing umbilical, the computer software calculates the sub-surface length of the tubing umbilical.
An embodiment of the software includes a memory module, a monitoring module, and a calculating module. Calculated values, as well as data relating to tubing properties, well trajectory and other constant values, are stored in the memory module. The monitoring module receives temperature, pressure and tension information, and well surveys from downhole and surface sensors via the telemetry system. The calculating module determines the sub-surface tubing umbilical length by retrieving the relevant information from the memory module and monitoring module. A preferred calculating module determines tubing umbilical length changes due to temperature differentials, hydraulic pressure differentials, and axial loadings on the tubing umbilical.
Another embodiment of the present invention includes logging while-drilling (LWD) package operated in conjunction with the preferred system. The LWD package logs formation properties such as gamma radiation and resistivity. A preferred system couples the logged formation data information to the calculated sub-surface tubing length. In still another embodiment, the present invention is deployed in conjunction with a casing collar or joint locator device that provides an accurate length measurement of distance traveled in a cased portion of a well bore. The measurements of the casing collar joint locator or similar device are used to verify or calibrate the calculations of the present invention.
Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.